The present invention relates to an apparatus for deferred handling of a message.
Publish and Subscribe (pub/sub) is an effective way of disseminating information to multiple users. Pub/Sub applications can help simplify the task of getting business messages and transactions to a wide, dynamically changing and potentially large audience in a timely manner.
In a pub/sub system such as WebSphere Message Broker (WebSphere is a registered trademark of International Business Machines Corporation), publishers are not concerned with where their messages are going, and subscribers are not interested in where the messages they receive have come from. Instead, a message broker typically assures the integrity of the message source and manages the distribution of a message according to subscriptions registered in the message broker.
Message topics typically provide the key to the delivery of messages between publishers and subscribers. With reference to a pub/sub system (100) as shown in FIG. 1A, instead of including a specific destination address in each message, a publisher (105) assigns a topic to a message. A message broker (110) comprises a matching engine (115) for matching a topic of a published message with a list of subscribers (120) who have subscribed to receive messages that are published to that topic. In response to a match, the message broker (110) sends the published message to the subscriber (120).
Topics are often associated with a hierarchical structure, known as a topic tree. An example of a topic tree is shown in FIG. 1B, wherein the topic tree comprises one root topic. Each character string in the topic tree represents a node of the topic tree. A complete topic is created by aggregating nodes from one or more levels in the topic tree. Levels are separated by a “/” character. The format of a folly specified topic is “root/level2/level3”. Valid topics in the topic tree are shown in FIG. 1B. Each topic can comprise data associated with particular locations, values etc.
It should be understood that the message broker (110) does not interpret or attempt to derive meaning from the topic. Rather, the message broker (110) uses the topic to send messages to subscribers who have subscribed to that topic.
In typical pub/sub systems, a topic associated with a message is specified by a publisher at the time of publishing the message. This is rather inflexible for publishers and it would be desirable to provide an improved apparatus.